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How ultraviolet radiation changes the protective functions of human skin

Beyond the well-documented DNA damage and cancer risk, ultraviolet rays can also change the way the cells in our outermost layer of skin hold together and respond to strain, according to new research from Stanford engineers.

In the study (subscription required), a team of researchers led by Reinhold Dauskardt, PhD, a professor in the Materials Science and Engineering Department at Stanford, subjected samples of human tissue to varying doses of UVB radiation, the range of ultraviolet wavelengths that are largely absorbed by the epidermis and don't penetrate deeper layers. The samples were later put under varying kinds of stress until they tore to test their mechanical limits. Study results showed that the sun takes a dramatic toll on our mechanical barrier function, makes it more prone to cracking and chapping and leaves deeper layers vulnerable to infection.

A Stanford release explains the findings and the study's importance from a global-climate and public-health perspective:

"UV exposure doesn't just make the stratum corneum weaker," said Dauskardt, "It also increases the actual stresses that cause the stratum corneum to fail. So it's sort of a double-whammy, which we didn't expect." In other words, UV radiation introduces more force driving skin cells apart while making the cells more helpless to resist.

This double threat is especially relevant to public health as global climate change will gradually change the way people interact with the sun. The spectrum of sunlight that penetrates to earth's surface is increasing, while warmer temperatures cause people to wear less clothing, making them more vulnerable.

Mechanical testing is also confirming the vital importance of wearing sunscreen to protect the skin's integrity. "It's totally cool," said Dauskardt, "You put a sunscreen on the sample and it causes a huge change in the way the skin is affected." This line of research offers a straightforward strategy for finding the best protection. Instead of trying to establish risk of carcinoma or gene damage, these methods can quickly and accurately model how different sun protection products affect the skin's mechanics. Dauskardt has already started comparative testing of sunscreens and thinks the work could be relevant in settling a currently raging debate about which types are most effective.

Previously: More evidence on the link between indoor tanning and cancers, Working to prevent melanoma, Intense, rapid sun tanning may increase skin cancer risk and California cities score below 50th percentile on 'sun-smart' survey
Photo by Ed Yourdon

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